1. Field of the Invention
This invention relates to wrenches and more particularly to wrenches that grip onto fastener heads such as nuts and bolts in order to prevent rounding of fastener-head corners and to grip previously rounded fastener heads or round objects such as pipes and rods.
2. Relation to Prior Art
Corners of fastener nuts and bolts often get rounded with wrenches that are loose-fitting, oversized, flexible, expandable or that do not contact enough surfaces and corners of fastener nuts and bolts to withstand rotational torque applied to them. Generally, most corner-rounding of fastener heads is caused by use of open-end wrenches and adjustable-size wrenches which are more versatile and, therefore, more readily available than limited-use box wrenches or socket wrenches. Some open-end wrenches are made thin for accessibleness but yield flexibly to high torque pressure and cause corner-rounding.
To assure snug fit of wrenches for preventing corner-rounding and to grip onto variously round objects of any kind, this wrench provides torque-actuated tightness of grip.
Examples of different but related wrenches not having the torque-actuated grip of fastener heads taught by this invention are described in the following patent documents. U.S. Pat. No. 4,510,825, issued to Neron et al, described a multi-mode wrench. U.S. Pat. No. 5,713,251, issued to Zurbuchen et al, described a glass-fiber-reinforced ratchet wrench. U.S. Pat. No. 5,542,322, issued to Knox et al, described a folding wrench for compactness. U.S. Pat. Nos. 4,819,521 and 4,748,875, issued to Lang, described a ratchet box wrench.
A known wrench for which a patent number is not known has torque-actuated grip different from this invention. It employs an internal swivel pawl in combination with three internal walls of a wrench head that are leveraged against three sides of a hex fastener head by rotational torque of the wrench. Its grasp of only three sides is not a wall-fitting grip of all sides in a manner taught by this invention. Further, the swivel pawl tends to round corners of a fourth side between fifth and sixth sides that are not contacted reliably by either the three internal walls or the swivel pawl.